1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to trip actuator assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to reset assemblies for circuit breaker trip actuator assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit.
Among other components, the operating mechanisms of some low-voltage circuit breakers, for example, typically include a pole shaft and a trip actuator assembly. The pole shaft pivots during opening and closing operations of the circuit breaker, which operations respectively correspond to electrical contact assemblies being opened (e.g., contacts separated) and closed (e.g., contacts electrically connected). The trip actuator assembly typically includes a trip bar, a trip actuator such as, for example, a solenoid, and a cradle assembly. The cradle assembly is coupled to and is cooperable with the pole shaft. The trip actuator (e.g., solenoid) has a spring, a coil which is energized by the trip unit in response to the electrical fault condition, and an actuating element such as, for example, a plunger. Normally (e.g., in the absence of the electrical fault condition), the plunger is latched (e.g., by a magnet) in a retracted position. When the coil is energized, in response to the electrical fault condition, the magnetic force that holds the plunger in the retracted position is overcome and the spring biases the plunger to an extended position and maintains it there. When the plunger extends, it causes the trip bar to pivot and trip open the electrical contact assemblies.
Subsequently, both the electrical contact assemblies and the trip actuator must be reset. The trip actuator assembly operates in conjunction with the pole shaft to perform the resetting operation. Specifically, when the circuit breaker operating mechanism is reset, the pole shaft pivots, thereby moving the cradle assembly. The cradle assembly then pivots a reset arm which, in turn, depresses the actuating element (e.g., plunger) and resets the trip actuator (e.g., solenoid).
The travel and actuating force of the plunger are relatively limited. Therefore, to ensure that the trip actuator assembly consistently performs properly, the trip actuator assembly must be well designed, and the trip actuator of this assembly must be accurately installed and maintained in a precise predetermined position within the circuit breaker.
In the above regard, known trip actuator assemblies suffer from a number of disadvantages. Among them is the fact that at least one component of the trip actuator assembly and, in particular, the trip actuator, is typically fastened to a portion of the circuit breaker that has no correlation to the tripping and/or resetting function(s) of the circuit breaker. This, alone or in combination with the fact that the trip actuator is typically fastened to such portion using hardware (e.g., brackets) and a plurality of fasteners, can result in misalignment of the trip actuator. In other words, misalignment of the trip actuator can result not only from the positioning of the hardware and trip actuator during its installation, but also from the fact that each component of the circuit breaker tends to vary in precise dimension due, for example, to manufacturing tolerances. When the circuit breaker is assembled, the tolerance variations from one part of the circuit breaker to the next can undesirably accumulate or “stack” up. Consequently, the accuracy with which the trip actuator is installed can be compromised, adversely affecting circuit breaker performance.
The aforementioned misalignment between circuit breaker components can also adversely affect the reset operation of the trip actuator assembly of known circuit breakers. For example, because the pole shaft, the cradle assembly, and the reset lever are coupled together, dimensional variations and/or assembly errors can result in imprecise interaction among these components. By way of example, the pole shaft and the cradle assembly may, for example, move in a manner which tends to over-rotate the reset lever of the trip actuator reset assembly. More specifically, over-rotation occurs when the reset lever has completely depressed the plunger, thus resetting the trip actuator, but the pole shaft and/or the cradle assembly continue to move causing the reset lever to continue to apply pressure to the plunger. It is desirable, therefore, to provide a trip actuator reset assembly that is capable of accommodating such over-rotation.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in trip actuator reset assemblies therefor.